Variable valve timing system for an internal combustion engine

ABSTRACT

An engine with a valve actuator to extend duration of a valve event and method of controlling an engine with such an actuator are disclosed. The actuator may include an actuator cylinder with an actuator piston. The actuator contains an electrorheological fluid. A magnetic flux may be applied the electrorheological fluid to prevent or slow movement of the actuator piston and change valve movement with respect to its regular, cyclical operation provide for with a cam. A biasing means is connected with the actuator piston to allow positioning of the valve actuator in an existing engine design.

TECHNICAL FIELD

[0001] This disclosure relates generally to internal combustion enginesand, more particularly, to an apparatus for varying valve timing.

BACKGROUND

[0002] The operation of an internal combustion engine requires, amongother things, the timed opening and closing of a plurality of valves.For example, with a typical four-stroke engine, one of ordinary skill inthe art will readily recognize such an engine operates through fourdistinct strokes of a piston reciprocating through a cylinder, withintake and exhaust valves operating in conjunction with the piston. Inan intake stroke, the piston moves from top dead center (TDC) where thepiston is near a head portion to bottom dead center (BDC) where thepiston is at a predetermined distance from the head. An intake valve isopened allowing air or a fuel and air mixture into the cylinder as thepiston travels from TDC to BDC. In a subsequent compression stroke, thepiston moves from BDC to TDC while both an exhaust valve and intakevalve inhibit gas flow from the cylinder, thereby compressing the airand any residual gasses within the cylinder. A combustion or powerstroke follows the compression stroke wherein fuel is injected into thecompressed air and thereby ignited. Alternatively, an ignition devicesuch as a spark plug may ignite the mixture of fuel and air. The forceresulting from the combustion pushes the piston toward BDC while boththe intake and exhaust valves are closed. Finally, the piston reversesdirection and moves back toward TDC with the exhaust valve open, therebypushing the combustion gases out of the cylinder.

[0003] Historically, valves on internal combustion engines have beenoperated in a regular cyclical fashion through the operation of a cammechanically connected to the valves. Mechanical operation provides anefficient transfer of energy. However, advanced engine cycles mayrequire at least temporary changes in the regular cyclical operation.

[0004] As an example, a Miller cycle in an internal combustion enginemay be desired to reduce the compression work while maintaining adesired expansion ratio. One method of operating an engine in a Millercycle closes an intake valve later than provided for by regular cyclicaloperation of a cam. The exhaust valve may also close later than providedfor by the cam to provide internal exhaust gas recirculation (EGR). Asknown by those skilled in the art, EGR reduces the oxygen available forcombustion and reduces formation of an uncertain form of oxides ofnitrogen (NOx).

[0005] In U.S. Pat. No. 6,237,551 issued to Macor et al. on May 29,2001, a system is described to vary a duration the valve is in an openposition. The cam is connected to a rocker arm to cyclically operate avalve. A hydraulic linkage is placed between the rocker arm and thevalves. When activated, the hydraulic linkage allows the rocker arm tomove the valve according to a profile of the cam. This system, may alsobe called a “lost motion” system, allows the valve duration to beshortened by decoupling the cam movement from the valve actuation. Thedecoupling of the valve from cam allows the valve to return to a valveseat or closed position earlier than produce by the cam movement.However, accidental decoupling or loss of hydraulic pressure will letall valves return to their closed position. The engine in turn will notbe able to operate.

[0006] As an alternative an actuating mechanism may instead alter thevalve movement by acting against the valve to hold the valve as shown inU.S. Pat. No. 6,321,706 issued to Wing on Nov. 27, 2001. In normaloperation, the cam cyclically operates on the valve. However, theregular cyclical operation may be altered to extend duration of valve inits open position through the use of various valve holding devices. Inone embodiment, a valve member has a shaft extending through amagneto-rheological fluid placed in a sealed chamber. The shaft includesan enlarged portion positioned within the sealed chamber. The valveclosing may be delayed by energizing a magnetic field near the chamberto increase the resistance against the enlarged portion moving throughthe magneto-rheological fluid and delaying closing of the valve.

[0007] The valve holding device of Wing requires a specifically designedvalve shaft and spring arrangement.

[0008] The present disclosure is directed to overcoming one or more ofthe problems or disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

[0009] In one aspect of the present invention an engine valve actuatorfor varying valve timing includes an actuator cylinder. Anelectromagnetic coil connects with the actuator cylinder. An actuatorpiston is reciprocatingly disposed in the actuator cylinder. A biasingmeans is connected with the actuator piston. An electrorheological fluidis disposed in at least a portion of the actuator cylinder.

[0010] In another aspect of the present invention an internal combustionengine includes a cam connecting with an intake valve and exhaust valveto cyclically move the valves. An engine valve actuator connects withintake valve. The engine valve actuator includes an actuator cylinder.An actuator piston is reciprocatingly positioned in the actuatorcylinder along with an electrorheological fluid. An electromagnetic coilis positioned in close proximity with the electrorheological fluid. Abiasing means is connected with the actuator piston.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is cross-sectional view of an engine having an engine valveactuator with an embodiment of the present invention;

[0012]FIG. 2 is a schematic representation an engine valve actuatorhaving an embodiment of the present invention;

[0013]FIG. 3 is a schematic representation of an engine valve actuatorhaving another embodiment of the present invention;

[0014]FIG. 4 is a graph plotting valve lift vs. engine crank angleduring normal operation;

[0015]FIG. 5 is a graph plotting valve lift vs. engine crank angleduring internal exhaust gas recirculation operation; and

[0016]FIG. 6 is a graph plotting valve lift vs. engine crank angleduring Miller cycle operation.

DETAILED DESCRIPTION

[0017] Referring now to the drawings, and with specific reference toFIG. 1, an embodiment of an internal combustion engine is generallyreferred to by reference numeral 20. While the engine 20 is depicted andwill be described in further detail herein with reference to a fourstroke, internal combustion diesel engine, it is to be understood thatthe teachings of the disclosure can be employed in conjunction with anyother type of reciprocating engine such as spark ignited engines,two-stroke engines, or rotary engines.

[0018] The engine 20 may include a plurality of engine cylinders 22 ineach of which is reciprocatingly mounted an engine piston 24. As knownin the art, the engine 20 may include any number of cylinders and may bearranged in various manners such as, for example, in-line or “V”. Aconnecting rod 26 connects with each engine piston 24, and in turnconnects to a crank shaft 27 so as to capitalize on the motion of theengine piston 24 to produce useful work in a machine (not shown) withwhich the engine 20 is associated. Each engine has an engine block 28defining the cylinder 24 and a cylinder head 30.

[0019] A pair of exhaust ports 38 and intake ports (not shown) may beprovided in the cylinder head 30 to allow for fluid communication intoand out of the engine cylinder 22. In normal engine operation, air maybe allowed to enter the engine cylinder 22 through the intake ports,while combustion or exhaust gases may be allowed to exit the enginecylinder 22 through the exhaust ports 38. An exhaust valve 42 may beprovided within each gas port. As shown the exhaust ports 38 and exhaustvalves 42 will be described in relation to an exhaust system. However,it should be understood that the intake ports and intake valve elementact in similar manner as known in the art.

[0020] Each of the exhaust valves 42 may include a valve head 44 fromwhich a valve stem 46 extends. The valve head 44 includes a sealingsurface 48 adapted to seal against a valve seat 50 about a perimeter 52of the valve ports 38. A bridge 54 is adapted to contact the valve stems46 of the valve 42. A valve spring 56 imparts force between the top ofeach valve stem 46 and the cylinder head 30, thereby biasing the stem 46away from the cylinder head 30 and thus biasing the valve head 44 intoseating engagement with the corresponding valve seats 50 or move theexhaust valve 42 into a closed position blocking the exhaust port 38.

[0021] Movement of the exhaust valve 42 is controlled not only by thesprings 56, but by a cam assembly 58 as well. As one of ordinary skillin the art will readily recognize, rotation of the cam 60 cyclicallycauses a push rod 62 to rise, thereby causing a rocker arm 64, connectedthereto, to pivot about a pivot 66. In so doing, an end 68 of the rockerarm 64 is caused to move downwardly and thereby move the exhaust valveelement 42 to an open position unblocking the exhaust port 38. Undernormal engine operation, the cam 60 imparts sufficient force to thevalve stem 46 to overcome the biasing force of the spring 56 and therebypush the valve head 44 away from the valve seat 50, to move the exhaustvalve 42 to an open position. Further rotation of the cam 60 allows thespring 56 to push the end 68 of the rocker arm 64 upward and the pushrod 62 downward until the cam 60 completes another revolution.Alternatively, the cam 60 may act directly on either the rocker arm 64or valve element 42 in a conventional manner.

[0022] In certain modes of engine operation, such as with thecompression release braking, Miller cycle operation, and EGR referencedabove, it is desirable for the exhaust valves 42 to be held in the openposition for longer periods, or at a timing sequence other than thatdictated by the cam 60. In such situations, an engine valve actuator 70may be used to so hold the exhaust valve 34 in the open position.

[0023] As shown in FIG. 2, the engine valve actuator 70 includes anactuator piston 72 reciprocatingly positioned in an actuator cylinder74. The actuator piston has an actuating surface 76 opposite a controlsurface 78. An actuating rod 80 may extend from the actuating surface 76through an opening 82 in the actuating cylinder 74 to engage theactuator arm 68. In this embodiment, a spring 84 attaches to the controlsurface 78 as a biasing means to urge the actuating piston to engagewith the exhaust valves 42. Any conventional biasing means may be usedsuch as a pressurized hydraulic or pneumatic cylinder that may bepassively or actively controlled. An electromagnetic coil 86 isconnected with the actuator cylinder 74. The electromagnetic coil 86 maybe any conventional device capable of generating a magnetic flux orelectric current operatively associated with an electrorhelologicalfluid 88. As shown, the electromagnetic coil 86 may be integral withactuator cylinder 74. The electrorehological fluid 88 is containedwithin the actuator cylinder 74. The electrorheological fluid 88includes magnetorheological fluids and other any fluid where viscositymay be controllable in response to controlling an applied magnetic fluxor electrical current. The electrorheological fluid 88 may pass from theactuating surface 76 to the control surface 78 via flow control device90 represented by a plurality of orifices in the present embodiment. Anelectronic controller 92 is connected with the electromagnetic coils 86.

[0024] An alternative engine valve actuator 70′ shown in FIG. 3 includesthe actuator piston 72′, a control piston 94, the actuator cylinder 74′,and a control cylinder 96 (where the “′” represents a componentcorresponding to an element of the embodiment shown in FIG. 2). Thecontrol piston 94 is reciprocatingly positioned in the control cylinder96. The spring 84′ or similar biasing means positions the control piston94 so as to reduce a control volume 98 in the control cylinder 96 forthe electrorheological fluid 88. In this embodiment, theelectrorheological fluid 88 is in fluid contact with the control surface78 of the actuator piston 72′. The actuator cylinder 74′ and controlcylinder 96 may be formed from a single cylinder 100 separated by apartition 102. The flow control device 90′, represented by an orifice inthis embodiment, is positioned in the partition 102. The flow controldevice 90′ allows the electrorhelogoical fluid 88 to fluidly communicatebetween the control cylinder 96 and the actuator cylinder 74′. Whilethis embodiment shows an orifice, any conventional flow control device90′ may be used. The electromagnetic coils 86′ in this embodiment areshown as being attached to the single cylinder 100.

Industrial Applicability

[0025]FIG. 4 shows a typical trace of an exhaust valve 42 when operatedusing the cam assembly 58. Each valve opens and closes in a regular,cyclical fashion (i.e. at a predetermined crank angle for each enginecycle.) Alternative engine cycles such as internal EGR and Miller cycleoperation require alteration of the regular, cyclical cam operation. Inthe present invention, the engine valve actuator 70 may be used withexisting engine designs without modifying existing components.

[0026] Taking internal EGR shown in FIG. 6, moving the exhaust valve 42to the closed position may be delayed by sending a signal to theelectromagnetic coil 86. During an exhaust stroke, as the piston 24moves toward TDC, the cam will cause the exhaust valve 34 to move awayfrom the seat 50. To prevent the exhaust valve from following the cammotion, a signal is sent by the controller 92 to establish a magneticflux (not shown) in the electrorhelogical fluid 88 causing the viscosityto increase. Motion of the actuator piston 72 is slowed or stopped bythe increased resistance due to the change in viscosity. At such timethe exhaust valve 34 is desired to return to its seat 50, the controller92 terminates the signal to reduce or eliminate the magnetic flux. Theexhaust valve 42 returns to its seat 50. The flow control device 90provides dampening to the actuator piston 72.

[0027] Continuing with the example of EGR, when the exhaust valve 34 isheld in the open position as the engine piston 24 ascends to a TDCposition, and remains in the open position after the engine piston 24reverses and descends. A portion of the exhaust gases vented fromneighboring engine cylinders 22 through the exhaust ports 36 are therebyreintroduced to the engine cylinder 22 by the resulting pressuredifferential. After a predetermined stroke length (e.g., ninety degreesof a seven hundred and twenty degree four stroke cycle), the exhaustvalve 42 is in the closed position, while the intake valve remains inthe open position to complete the intake stroke as explained above.

[0028] The teachings of the present disclosure can also be used toprovide Miller cycle benefits. As illustrated in FIG. 6, the intakevalves may be held open during the initial stages of the compressionstroke to thereby reduce the compression work of the engine 20 andprovide the engine efficiencies of the Miller cycle as well known bythose of ordinary skill in the art. The intake valve could be so held byemploying the engine actuator 70 after the cam assembly 58 moves theintake valve to the open position during the intake stroke. Morespecifically, as the intake valve is about to be moved to the closedposition by the spring 56 at the conclusion of a normal intake stroke,the electromagnetic coil 86 could be actuated so as to slow movement ofthe actuator piston and thereby the intake valve toward the seat 50.

[0029] Other aspects and features of the present disclosure can beobtained from a study of the drawings, the disclosure, and the appendedclaims.

What is claimed is:
 1. An engine valve actuator, comprising: an actuatorcylinder; a electromagnetic coil connected with at least a portion ofsaid actuator cylinder; an actuator piston reciprocatingly disposed insaid actuator cylinder, said actuator piston having an actuating surfaceand a control surface opposite said actuating surface; a biasing meansbeing operatively connected with said control surface; and anelectrorheological fluid disposed in at least a portion of said actuatorcylinder.
 2. The engine valve actuator of claim 1 including a flowcontrol device fluidly connecting said actuating surface with saidcontrol surface.
 3. The engine valve actuator of claim 2 wherein saidcontrol device is an orifice in said actuator piston.
 4. The enginevalve actuator of claim 1 wherein said biasing means is a springconnected between said control surface and said actuator cylinder. 5.The engine valve actuator of claim 1 wherein said electromagnetic coilis integral with said actuator cylinder.
 6. The engine valve actuator ofclaim 1 wherein said biasing means includes: a control pistonreciprocatingly positioned in said actuating cylinder, said controlpiston having a second biasing means, said control piston being adaptedto reduce a control volume in said actuating cylinder; and a flowcontrol device fluidly connecting said control piston with said controlsurface.
 7. The engine valve actuator of claim 6 wherein said secondbiasing means is a spring connecting between said control piston andsaid actuating cylinder.
 8. The engine valve actuator of claim 6 whereinsaid control device is an orifice.
 9. An engine valve actuator,comprising: an actuator cylinder; an actuator piston reciprocatinglydisposed in said actuator cylinder; an electromagnetic coil connectingwith at least a portion of said actuator cylinder; an electrorheologicalfluid disposed in at least a portion of said actuator cylinder; acontrol cylinder fluidly connecting with said actuator cylinder througha flow control device; a control piston reciprocatingly disposed in saidcontrol cylinder; and a biasing means being operatively connected withsaid control piston, said biasing means being adapted expel saidelectrorheological fluid from said control cylinder.
 10. The enginevalve actuator of claim 9 wherein said biasing means is a spring. 11.The engine valve actuator of claim 9 wherein said actuator cylinder andsaid control cylinder are formed by a single cylinder divided by apartition.
 12. The engine valve actuator of claim 11 wherein saidcontrol device is an orifice in said partition.
 13. An internalcombustion engine having valves with variable timing, said enginecomprising: an engine block defining an engine cylinder; a pistonreciprocatingly positioned in said engine cylinder; a cylinder headbeing connected with said engine block, said head defining an inlet portand an exhaust port; an intake valve positioned in said inlet port, saidvalve being adapted to restrict flow through said intake port to saidcylinder; an exhaust valve positioned in said exhaust port, said valvebeing adapted to restrict flow through said exhaust port to saidcylinder; a cam being connected with said intake valve and said exhaustvalve to cyclically move said intake valve and said exhaust valve; andan engine valve actuator connected with said intake valve, said valveactuator including: an actuator cylinder having an actuator pistonreciprocatingly positioned in said actuator cylinder, anelectrorheological fluid being contained in said actuator cylinder, anelectromagnetic coil being proximate said electrorheological fluid, anda biasing means being connected with a control surface of said actuatorpiston.
 14. The engine of claim 13 wherein said biasing means is aspring.
 15. The engine of claim 13 wherein said biasing means includes:a control cylinder; a control piston reciprocatingly positioned in saidcontrol cylinder; and a second biasing means being connected with saidcontrol piston, said biasing means being adapted to reduce a controlvolume in fluid communication with said control surface.
 16. The engineof claim 15 including a flow control device between said control volumeand said control surface.
 17. The engine of claim 13 including acontroller being connected with said engine valve actuator.